The overall aim of this project is to determine the pathophysiology of non-alcoholic steatohepatitis (NASH) and specifically to determine whether the hepatic synthesis of VLDL apoB-100 is attenuated in patients with NASH, causing defective removal of synthesized triglycerides from hepatocytes. The specific aim is to measure the postabsorptive fractional synthesis rate of VLDL apoB-100 in subjects with histologically proven NASH and to compare this to the FSR of VLDL apo-B 100 in two control groups: 1) an equal number of body mass index, gender, and age-matched healthy subjects without NASH; and 2) an equal number of lean, gender and age-matched healthy control subjects without NASH.